加载了一个文档列表,用户只能打开每个文档的一个实例,但可以同时打开多个不同的文档.打开1个文档时打开,保存和关闭没有任何问题,但是,当他们同时打开多个文档时,关闭我的任何Word实例时出现以下错误：

The file is in use by another application or user. (C:\...\Templates\Normal.dotm) 
This error is commonly encountered when a read lock is set on the file that you are attempting to open.

我使用以下代码打开文档并处理BeforeDocumentClosed事件：

public void OpenDocument(string filePath,Protocol protocol,string docTitle,byte[] document)
{
    _protocol = protocol;
    documentTitle = docTitle;
    _path = filePath;

    if (!_wordDocuments.ContainsKey(_path))
    {
        FileUtility.WriteToFileSystem(filePath,document);

        Word.Application wordApplication = new Word.Application();
        wordApplication.DocumentBeforeClose += WordApplicationDocumentBeforeClose;

        wordApplication.Documents.Open(_path);

        _wordDocuments.Add(_path,wordApplication);
    }
    _wordApplication = _wordDocuments[_path];
    _currentWordDocument = _wordApplication.ActiveDocument;

    ShowWordApplication();
}

public void ShowWordApplication()
{
    if (_wordApplication != null)
    {
        _wordApplication.Visible = true;
        _wordApplication.Activate();
        _wordApplication.ActiveWindow.SetFocus();
    }
}

private void WordApplicationDocumentBeforeClose(Document doc,ref bool cancel)
{
    if (!_currentWordDocument.Saved)
    {
        DialogResult dr = MessageHandler.ShowConfirmationYnc(String.Format(Strings.DocumentNotSavedMsg,_documentTitle),Strings.DocumentNotSavedCaption);

        switch (dr)
        {
            case DialogResult.Yes:
                SaveDocument(_path);
                break;
            case DialogResult.Cancel:
                cancel = true;
                return;
        }
    }

    try
    {
        if (_currentWordDocument != null)
            _currentWordDocument.Close();
    }
    finally
    {
        Cleanup();
    }
}

public void Cleanup()
{
    if (_currentWordDocument != null)
        while(Marshal.ReleaseComObject(_currentWordDocument) > 0);

    if (_wordApplication != null)
    {
        _wordApplication.Quit();
        while (Marshal.ReleaseComObject(_wordApplication) > 0);
        _wordDocuments.Remove(_path);
    }
}

有没有人看到我正在做的任何错误,允许同时打开多个文件？我是Word Automation和Word Interop服务的新手,所以任何建议都表示赞赏.谢谢.